feat(shell): enable more plugins and give agent shells a light theme

Uncomment history-substring-search, systemd, k, extract, and sudo, and add
poetry to the default plugin list; all are installed via the bundled or custom
plugin dirs. Switch to robbyrussell when CURSOR_AGENT is set so Cursor's agent
terminal skips powerlevel10k, keeping interactive shells on p10k.

Co-authored-by: Cursor <cursoragent@cursor.com>

.zshrc

@@ -16,7 +16,13 @@ export ZSH=$HOME/.oh-my-zsh
 # it'll load a random theme each time that oh-my-zsh is loaded.
 # See https://github.com/robbyrussell/oh-my-zsh/wiki/Themes
 
-ZSH_THEME="powerlevel10k/powerlevel10k"
+# Agent/AI terminals (Cursor's agent sets CURSOR_AGENT) get a light, fast theme;
+# interactive shells use powerlevel10k.
+if [[ -n "$CURSOR_AGENT" ]]; then
+    ZSH_THEME="robbyrussell"
+else
+    ZSH_THEME="powerlevel10k/powerlevel10k"
+fi
 
 # Uncomment the following line to use case-sensitive completion.
 # CASE_SENSITIVE="true"
@@ -64,12 +70,13 @@ plugins=(
     # zsh-completions   INSTALL METHOD CHANGED https://github.com/zsh-users/zsh-completions/issues/603
     zsh-autosuggestions
     zsh-syntax-highlighting
-    # history-substring-search
+    history-substring-search
-    # systemd
+    systemd
-    # k
+    k
-    # extract
+    extract
-    # sudo
+    sudo
     fzf-tab
+    poetry
     # web-search
     # httpie
     # git